Semiconductor device with a buried stressor

ABSTRACT

A semiconductor device, such as a PMOS or NMOS device, having localized stressors is provided. Recesses are formed on opposing sides of a gate electrode. A stress-inducing region is formed along a bottom of the recess, and a stressed layer is formed over the stress-inducing region. By having a stress-inducing region with a larger lattice structure than the stressed layer, a tensile strain may be created in a channel region of the semiconductor device and may be suitable for an NMOS device. By having a stress-inducing region with a smaller lattice structure than the stressed layer, a compressive strain may be created in the channel region of the semiconductor device and may be suitable for a PMOS device. Embodiments may be applied to various types of substrates and semiconductor devices, such as planar transistors and finFETs.

TECHNICAL FIELD

This disclosure relates generally to semiconductor devices and, moreparticularly, to semiconductor devices having a buried stressor andmethods of manufacture.

BACKGROUND

Size reduction of metal-oxide-semiconductor field-effect transistors(MOSFETs), including reduction of the gate length and gate oxidethickness, has enabled the continued improvement in speed, performance,density, and cost per unit function of integrated circuits over the pastfew decades. To further enhance transistor performance, MOSFET deviceshave been fabricated using strained channel regions located in portionsof a semiconductor substrate. Strained channel regions allow enhancedcarrier mobility to be realized, thereby resulting in increasedperformance when used for n-channel (NMOSFET) or for p-channel (PMOSFET)devices. Generally, it is desirable to induce a tensile strain in then-channel of an NMOSFET transistor in the source-to-drain direction toincrease electron mobility and to induce a compressive strain in thep-channel of a PMOSFET transistor in the source-to-drain direction toincrease hole mobility. There are several existing approaches ofintroducing strain in the transistor channel region.

In one approach, strain in the channel is introduced by creating arecess in the substrate in the source/drain regions. For example, a PMOSdevice having a compressive stress in the channel region may be formedon a silicon substrate by epitaxially growing a stress-inducing layerhaving a larger lattice structure than the silicon, such as a layer ofSiGe, within recessed regions in the source/drain regions. Similarly, anNMOS device having a tensile stress in the channel region may be formedon a silicon substrate by epitaxially growing a stress-inducing layerhaving a smaller lattice structure than the silicon, such as a layer ofSiC, within recessed regions in the source/drain regions.

These other materials such as SiGe and SiC, however, may cause otherissues with regard to the device. For example, using these non-Simaterials in the source/drain regions may cause challenges in eithersilicidation or ultra-shallow junction formation. For example, using aGe layer or a layer of SiGe material having a high percentage of Ge forPMOS devices may cause rapid B diffusion problems, and SiC layers mayexhibit dopant deactivation issues. These limitations may create issueswith, and possibly prevent, realization of the full potential of thestressor for aggressively scaled devices.

SUMMARY

These and other problems are generally reduced, solved, or circumvented,and technical advantages are generally achieved, by embodimentsdiscussed herein, which provides a strained semiconductor device toimprove the operating characteristics of the semiconductor device and amethod of manufacture.

In an embodiment, a semiconductor device, such as a planar PMOS or NMOStransistor, having localized stressors is provided. Recesses are formedon opposing sides of a gate electrode. A stress-inducing region isformed along a bottom of the recess, and a stressed layer is formed overthe stress-inducing region. By having a stress-inducing region with alarger lattice structure than the stressed layer, a tensile strain maybe created in a channel region and may be suitable for an NMOS device.By having a stress-inducing region with a smaller lattice structure thanthe stressed layer, a compressive strain may be created in the channelregion of the semiconductor device and may be suitable for a PMOSdevice.

In another embodiment, a semiconductor device, such as an NMOS or a PMOSfinFET, is provided. A semiconductor fin is recessed and astress-inducing layer is formed on a top surface of the recessed fin. Astressed fin is formed over the stress-inducing layer. An NMOS finFEThaving a tensile strain in a channel region may be formed by using amaterial for the stress-inducing region with a larger lattice structurethan the material of the stressed fin, and a PMOS finFET having acompressive strain in the channel region may be formed by using amaterial for the stress-inducing region with a smaller lattice structurethan the material of the stressed fin.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a stress-inducing region having a relatively largelattice structure in accordance with an embodiment;

FIG. 2 illustrates a stress-inducing region in equilibrium in accordancewith an embodiment;

FIG. 3 illustrates a stress-inducing region having a relatively smalllattice structure in accordance with an embodiment;

FIGS. 4-8 illustrate various process steps of fabricating asemiconductor device having a stressed channel region in accordance withan embodiment; and

FIGS. 9-13 illustrate various process steps of fabricating asemiconductor device having a stressed channel region in accordance withanother embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments are discussed in detail below.It should be appreciated, however, that the embodiments provide manyapplicable inventive concepts that can be embodied in a wide variety ofspecific contexts. The specific embodiments discussed are merelyillustrative of specific ways to make and use the embodiments, and donot limit the scope of the disclosure.

As will be explained in greater detail below, embodiments utilize aburied stress-inducing layer having a different lattice structure thanan overlying layer. The difference in the lattice structure between thestress-inducing layer and the overlying layer will cause the overlyinglayer to have either a compressive stress or a tensile stress. When usedin source/drain regions of a transistor, the stress-inducing layer maybe used to create the desired stress in a channel region, while stillallowing for silicon in upper surfaces of source/drain regions.

For example, FIG. 1 illustrates an example of an embodiment in which astress-inducing layer 102 has a lattice structure larger than anoverlying stressed layer 104, thereby exerting a tensile stress in achannel region 106 between a source region 108 and a drain region 110.In this example, the stress-inducing layer 102 is placed in the sourceregion 108 and the drain region 110, and the stressed layer 104 isformed over the stress-inducing layer 102. A lattice structure of thestress-inducing layer 102 is larger than a lattice structure of thestressed layer 104. As a result of this difference in the latticestructure, the stressed layer 104 has a tensile stress as the latticestructure of the stressed layer 104 is stretched to match the latticestructure of the stress-inducing layer 102. The tensile stress in thesource region 108 and the drain region 110 in turn causes the channelregion 106 to have a tensile stress as indicated by the arrows in FIG.1.

It should be noted that FIG. 1 illustrates an example that is not atequilibrium for purposes of better illustrating the stress directions.FIG. 2 illustrates an example of the embodiment discussed above withreference to FIG. 1 wherein the lattice structure is shown withoutequilibrium and after equalization. In this example, Ge is used as anexample of a material with a lattice structure larger than the latticestructure of Si.

While FIG. 1 illustrates an example in which the channel region 106 hasa tensile stress, which is suitable for an NMOS device, FIG. 3illustrates an example of an embodiment in which the channel region 106has a compressive stress, which may be more suitable for a PMOS device.In this example, the stress-inducing layer 102 has a smaller latticestructure than the lattice structure of the overlying stressed layer104. This difference will cause a compressive stress in the stressedlayer 104 as the lattice structure of the stressed layer 104 iscompressed to match the lattice structure of the stress-inducing layer102. This compressive stress in the source region 108 and the drainregion 110 causes the channel region 106 to have a compressive stress asindicated by the arrows in FIG. 3. It should be noted that FIG. 2, onecase illustrates an example that is not at equilibrium for purposes ofillustration to better illustrate the stress directions.

FIGS. 4-8 illustrate a method for fabricating a semiconductor devicehaving a strained channel region in accordance with an embodiment.Referring first to FIG. 4, a portion of a substrate 400 having isolationregions 402 formed therein is shown in accordance with an embodiment.The substrate 400 may comprise bulk silicon, doped or undoped, or anactive layer of a semiconductor-on-insulator (SOI) substrate. Generally,an SOI comprises a layer of a semiconductor material, such as silicon,formed on an insulator layer. The insulator layer may be, for example, aburied oxide (BOX) layer or a silicon oxide layer. The insulator layeris provided on a substrate, typically a silicon or glass substrate.Other substrates, such as a multi-layered or gradient substrate may alsobe used. The substrate may alternatively be a Ge substrate, a SiGesubstrate, a group III-V substrate, or the like.

The isolation regions 402, such as insulator-filled shallow trenchisolations, may be formed in an area of substrate 400 where physicalisolation of the MOSFET regions is desired. The isolation regions 402may comprise silicon oxide deposited by chemical vapor deposition (CVD)techniques. Other isolation structures, such as a thermally grown fieldoxide (FOX) region or the like, and other materials may also be used.

FIG. 4 further illustrates a gate structure 404 comprising a gateinsulator layer 410, a gate electrode 412, and spacers 414 formed andpatterned on the substrate 400. The gate insulator layer 410 may beformed of a high-K dielectric material, such as silicon oxide, siliconoxynitride, silicon nitride, an oxide, a nitrogen-containing oxide, acombination thereof, or the like. In an embodiment, the gate insulatorlayer 410 has a relative permittivity value greater than about 4. Otherexamples of such materials include aluminum oxide, lanthanum oxide,hafnium oxide, zirconium oxide, hafnium oxynitride, or combinationsthereof.

In an embodiment in which the gate insulator layer 410 comprises anoxide layer, the gate insulator layer 410 may be formed by any oxidationprocess, such as wet or dry thermal oxidation in an ambient comprisingan oxide, H₂O, NO, or a combination thereof, or by CVD techniques usingtetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. The gateinsulator layer 410 is about 10 Å to about 50 Å in thickness.

The gate electrode 412 may comprise a conductive material, such as ametal (e.g., tantalum, titanium, molybdenum, tungsten, platinum,aluminum, hafnium, or ruthenium), a metal silicide (e.g., titaniumsilicide, cobalt silicide, nickel silicide, or tantalum silicide), ametal nitride (e.g., titanium nitride or tantalum nitride), dopedpoly-crystalline silicon, other conductive materials, or a combinationthereof. In one example, amorphous silicon is deposited andrecrystallized to create poly-crystalline silicon (poly-silicon). In anembodiment in which the gate electrode is poly-silicon, the gateelectrode 412 may be formed by depositing doped or undoped poly-siliconby low-pressure CVD (LPCVD) to a thickness in the range of about 200 Åto about 1000 Å.

The gate insulator layer 410 and the gate electrode 412 may be patternedby photolithography techniques as are known in the art. Generally,photolithography involves depositing a photoresist material, which isthen masked, exposed, and developed. After the photoresist mask ispatterned, an etching process may be performed to remove unwantedportions of the gate dielectric material and the gate electrode materialto form the gate insulator layer 410 and the gate electrode 412 asillustrated in FIG. 4. In an embodiment in which the gate electrodematerial is poly-crystalline silicon and the gate dielectric material isan oxide, the etching process may be a wet or dry, anisotropic orisotropic, etch process.

FIG. 4 also illustrates the formation of spacers 414. As is known in theart, to form spacers 414, a gate spacer layer (not shown) is firstformed. In an embodiment, the gate spacer layer includes a nitride layeron an oxide layer. In alternative embodiments, the gate spacer layer mayinclude a single layer or more than two layers, each comprising oxide,silicon nitride, silicon oxynitride (SiON), and/or other dielectricmaterials. The gate spacer layer may be formed using commonly usedtechniques, such as plasma enhanced CVD (PECVD), low-pressure CVD(LPCVD), sub-atmospheric CVD (SACVD), and the like. The gate spacerlayer is then patterned to form spacers 414, wherein the patterning maybe performed by either wet etching or dry etching. Horizontal portionsof the spacer layer are removed, and the remaining portions form spacers414.

Referring to FIG. 5, recesses 502 are formed on opposing sides of thegate electrode 412. As discussed in greater detail below, astress-inducing layer will be epitaxially grown along the bottom of therecesses 502, and a stressed layer will be epitaxially grown over thestress-inducing layer. In accordance with an embodiment, the recesses502 have a depth such that the stress-inducing layer can be grown to athickness sufficient to result in a surface free of dislocations due tolattice mismatch between the stress-inducing layer and the material ofthe underlying substrate. In this manner, the surface of thestress-inducing layer will be relaxed, thereby having a latticestructure substantially close to its intrinsic lattice structure.

For example, in an embodiment, recesses 502 may be etched by, forexample, HBr/O₂, HBr/Cl₂/O₂, or SF₆/Cl₂ plasma to a depth between about400 Å and about 3000 Å. One skilled in the art will realize that thedimensions provided throughout the description are merely examples, andthe dimensions may vary with the scaling of the technology used forforming the integrated circuits.

FIG. 6 illustrates the formation of stress-inducing regions 602 alongthe bottoms of the recesses 502. In an embodiment, the stress-inducingregions 602 are formed to a thickness such that surface of thestress-inducing regions 602 are free from dislocations as a result ofthe lattice mismatch between the material of the stress-inducing regions602 and the material of the underlying substrate 400, thereby resultingin stress-inducing regions 602 having a surface with a relaxed intrinsiclattice structure. As a result, the thickness of the stress-inducingregions 602 may be varied depending on the types of materials used.

FIG. 7 illustrates formation of stressed regions 702 overlying thestress-inducing regions 602 in accordance with an embodiment. Thematerial of the stressed regions 702 is selected such that a latticemismatch exists between the material of the stress-inducing regions 602and the material of the stressed regions 702. One of ordinary skill inthe art will also appreciate that the type of materials may be varieddepending upon the type of device being formed. For example, in formingan NMOS device, the stress-inducing regions 602 may be formed of SiGeand the stressed regions 702 may be formed of silicon, which has asmaller lattice structure than SiGe. The lattice structure of the SiGestress-inducing regions 602 causes a tensile stress in the stressedregions 702, which in turn causes a tensile strain in the channelregion, thereby increasing the electron mobility. SiGe stress-inducingregions 602 may be epitaxially grown in a selective epitaxial growth(SEG) process such as CVD using Si-containing gases and Ge-containinggases, such as SiH₄ and GeH₄, respectively, as precursors. Overlyingsilicon stressed regions 702 may be epitaxially grown in a SEG processsuch as CVD using Si-containing gases, such as SiH₄, as precursors.

In another example for forming a PMOS device, the stress-inducingregions 602 may be formed of SiC and the stressed regions 702 may beformed of silicon, which has a larger lattice structure than SiC. Thelattice structure of the SiC stress-inducing regions 602 causes acompressive stress in the stressed regions 702, which in turn causes acompressive strain in the channel region, thereby increasing the holemobility. SiC stress-inducing regions 602 may be epitaxially grown in aSEG process such as CVD using Si-containing gases, such as SiH₄, andC-containing gases, such as C₂H₄ or C₂H₆, as precursors. Overlyingsilicon stressed regions 702 may be epitaxially grown in a SEG processsuch as CVD using Si-containing gases, such as SiH₄, as precursors.

It should also be noted that other materials may be used for thesubstrate 400, the stress-inducing regions 602, and the stressed regions702. For example, substrates and/or the stressed region may be formed ofSiGe, Ge, a Group III-V material, or the like. In this example, thestress-inducing regions 602 may be formed of a material such as SiGe,Ge, or the like which have a lattice structure larger than that of thestressed region for an NMOS device and a material such as Si, SiC, orthe like which have a lattice structure smaller than that of thestressed region for a PMOS device.

It should be noted that the stressed regions 702 are illustrated to havean upper surface even with a bottom surface of the gate insulator layer410 for illustrative purposes only, and as such, the stressed regions702 may alternatively be raised above or recessed below the bottomsurface of the gate insulator layer 410. It should further be noted thatpart or all of one or both of the stress-inducing regions 602 and thestressed regions 702 may be in situ doped with impurities. For example,an NMOS device may be formed by doping the stress-inducing regions 602and/or the stressed regions 702 with N-type impurities such as arsenicor phosphorous, and a PMOS device may be formed by doping thestress-inducing regions 602 and/or the stressed regions 702 with P-typeimpurities such as boron. Alternatively, the stress-inducing regions 702may be doped with dopants of polarity opposite to that of the stressedregions 702, to help control short channel effect and improve isolation.

As one of ordinary skill in the art will appreciate, embodiments such asthose discussed above allow for a different material to be used in thesource/drain regions than the layer causing the stress. In theseembodiments, the stress-inducing regions 602 are buried beneath thestressed regions 702. This allows the material used in the stressedregions 702 to vary from the material used to actually induce thestrain, e.g., the stress-inducing regions 602. As a result, materialssuch as silicon may be used in the source/drain regions, allowingwell-developed silicidation and Si junction formation technology to bereadily applied on the stressed regions 702. Such a feature allows thestrain in the channel region to be adjusted by altering the type ofmaterial and the characteristics of the stress-inducing regions 602,without necessarily altering subsequent processing steps.

FIG. 8 illustrates the formation of source/drain regions 804 andsilicide regions 802 in accordance with an embodiment. It should benoted that the source/drain regions are generally represented by ovals.One of ordinary skill in the art will realize that embodiments disclosedherein may be used with any suitable source/drain doping profile,including any suitable use of spacers, liners, and/or sacrificialliners/spacers. For example, lightly-doped drains (LDD) may be formedprior to recessing the substrate 400, the heavily-doped regions may beformed in situ or after formation of the stressed regions 702 with theuse of the spacers 414 and/or different spacers and/or additionalspacers. As another example, both the LDD and the heavily-doped regionsmay be formed after forming recesses by, for example, in situ,implantation, diffusion, or the like.

As is known in the art, silicide regions 802 may be formed by blanketdepositing a thin layer of metal, such as nickel, platinum, cobalt, andcombinations thereof. The substrate is then heated, causing the siliconto react with the metal where contacted. After the reaction, a layer ofmetal silicide is formed. The un-reacted metal is selectively removedthrough the use of an etchant that attacks metal but does not attacksilicide.

It should also be noted that the location of the recesses 502 may bevaried. For example, the recesses may be offset from, aligned with, orextend under the gate electrode 412.

Thereafter, subsequent processing techniques well-known in the art maybe performed to complete the device. For example, one or more dielectriclayers and metallization layers may be formed, as well as back-end ofline (BEOL) processing techniques suitable for the particularapplication may be performed.

FIGS. 9-13 illustrate a method for fabricating a semiconductor devicehaving a strained channel region in a finFET device in accordance withan embodiment. Referring first to FIG. 9, a portion of a substrate 900having a fin 902 extending between isolation regions 904 is shown inaccordance with an embodiment. The substrate 900 may comprise bulksilicon, doped or undoped, or an active layer of an SOI substrate. Thesubstrate may alternatively be a Ge substrate, a SiGe substrate, a groupIII-V substrate, or the like. Other substrates, such as a multi-layeredor gradient substrate may also be used. The insulator layer may be, forexample, a silicon oxide layer.

As illustrated in FIG. 10, the fin 902 is recessed using, for example,an anisotropic etch process. As discussed in greater detail below, partof the fin is removed and replaced with a stress-inducing layer, uponwhich the fin will be reformed. In accordance with an embodiment, thefin is recessed to a depth such that the stress-inducing layer can begrown to a thickness sufficient to result in a surface free ofdislocations due to lattice mismatch between the stress-inducing layerand the material of the underlying substrate. In this manner, thesurface of the stress-inducing layer will be relaxed, thereby having itsintrinsic lattice structure. For example, in an embodiment, the fin 902is recessed by, for example, etching using HBr/O₂, HBr/Cl₂/O₂, orSF₆/Cl₂ plasma to a depth between about 400 Å and about 3000 Å.

FIG. 11 illustrates forming a stress-inducing region 1102. Thestress-inducing region 1102 may be formed in a similar manner usingsimilar materials as discussed above with reference to thestress-inducing regions 602 and FIG. 6.

Thereafter, as illustrated in FIG. 12, a stressed fin 1202 may be formedoverlying the stress-inducing region 1102. The stressed fin 1202 may beformed of similar materials using similar techniques as discussed abovewith reference to the stressed regions 702 and FIG. 7. However, in thisembodiment, the stressed fin 1202 is formed to a height above theisolation regions 904. In an embodiment, the stressed fin 1202 extendsbetween about 200 Å and about 1000 Å above the isolation regions 904.

It should be noted that other layers may be used to form the stressedfin 1202. For example, a mask layer may be formed over the isolationregions 904 to aid in the shaping of the stressed fin 1202, preventingor reducing the amount the stressed fin 1202 extends over a top surfaceof the isolation regions 904 during formation.

FIG. 13 illustrates the formation of source/drain regions 1304 andsilicide regions 1302 in accordance with an embodiment. It should benoted that the source/drain regions 1304 are generally represented byovals. One of ordinary skill in the art will realize that embodimentsdisclosed herein may be used with any suitable source/drain dopingprofile, including any suitable use of spacers, liners, and/orsacrificial liners/spacers.

It should be noted that FIGS. 9-13 illustrate an embodiment in which thesource/drain regions of the fin are removed and replaced with anunderlying stress-inducing region 1102. In other embodiments, however,the channel region may be recessed without recessing the source/drainregions. In this embodiment, the processes discussed above with respectto FIGS. 9-12 are performed in the channel region. Furthermore, inanother embodiment, the entire fin (e.g., both the channel region andthe source/drain regions) is recessed. In this embodiment, thesource/drain regions are formed as discussed above with reference toFIGS. 9-13 and the channel region is formed as discussed above withreference to FIGS. 9-12. It will be appreciated that in embodiments inwhich the channel region of the fin is being replaced, the doping mayvary.

Thereafter, subsequent processing techniques well-known in the art maybe performed to complete the device. Other processes may include forminga gate insulator, gate electrode, source/drain regions, one or moredielectric layers and metallization layers, BEOL processing, and thelike.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture,composition of matter, means, methods, and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

1. A method of forming a semiconductor device, the method comprising:providing a substrate having a fin extending from the substrate andisolation regions on opposing sides of the fin; recessing at least aportion of the fin below a top surface of the isolation regions; forminga stress-inducing region along a top surface of the recessed fin; andforming a stressed fin over the stress-inducing region.
 2. The method ofclaim 1, wherein the stress-inducing region has a lattice structurelarger than the stressed fin and the semiconductor device is an NMOSdevice.
 3. The method of claim 1, wherein the stress-inducing region hasa lattice structure smaller than the stressed fin and the semiconductordevice is a PMOS device.
 4. The method of claim 1, wherein the portionof the fin includes at least one of a source region and a drain regionof the fin.
 5. The method of claim 1, wherein the portion of the finincludes a channel region of the fin.
 6. The method of claim 1, whereinthe stress-inducing region is doped with dopants having an oppositepolarity as the stressed fin.